Drink eight glasses of water a day. Eight times eight ounces. Two litres minimum. Don't trust thirst, by the time you're thirsty you're already dehydrated. There is a water bottle on every desk in every office. There are smart bottles that vibrate to remind you. Your hairdresser will ask you about it. Your skin needs it, your kidneys need it, your brain needs it, and you should keep going past thirsty.
There's no scientific basis for the number eight. The most common origin trace points to a 1945 US Food and Nutrition Board recommendation that adults consume around 2.5 litres of water daily, with a footnote noting that 'most of this quantity is contained in prepared foods,' which is the part everyone forgot. About 20 percent of daily water intake comes from food (fruit, vegetables, soups, even bread). Tea, coffee, juice, milk all count. Adult kidneys are exceptionally good at maintaining hydration, and thirst is a reliable signal in healthy people. Drinking more than your body needs simply produces more urine. Excessive water intake (over 6 litres in a few hours) can cause hyponatraemia, which has killed marathon runners, military recruits, and at least one radio competition entrant. Specific groups (athletes during heat, pregnant women, people on certain medications, people with kidney disease) need more deliberate intake. The healthy office worker does not. Listen to thirst. Eat your fruit. Have a glass of water with meals. Don't carry around two litres like a hostage situation.